U.S. Pat. No. 4,454,801, issued Jun. 19, 1984, and assigned to the assignee of this invention, describes a motor vehicle power steering gear having a spool shaft connected to a steering wheel of the vehicle, a pinon head connected to a steered wheel of the vehicle, and a torsion bar between the spool shaft and the pinon head. A steering assist hydraulic boost pressure is regulated by a valve of the steering gear in response to rotation of the spool shaft from an on-center position thereof relative to the pinion head against a restoring force of the torsion bar.
In some power steering gears, the onset of power assist is delayed by a preload apparatus which prevents rotation of the spool shaft from its relative on-center position until manual steering effort exceeds a preload. Typically, such preload apparatus includes a C-shaped spring having a pair of resilient jaws, a drive pin on the spool shaft clamped with a preload between the resilient jaws of the C-shaped spring, and a rigid abutment on the pinon head which is aligned with the drive pin in the relative on-center position of the spool shaft and, likewise, clamped with the preload between the resilient jaws of the C-shaped spring. Such steering gears may encounter an operating condition in which the pinion head is forced by irregularities in the road surface to oscillate back and forth across the relative on-center position of the spool shaft. In that circumstance, the rigid abutment may audibly impact alternate ones of the resilient jaws of the C-shaped spring as the pinion head is forced back and forth across the relative on-center position of the spool shaft.